The Audi has the smallest engine of those three in terms of displacement with its 4.0-litre twin-turbo V8 engine not quite measuring up to the 5.5 litres (Benz) and 4.4 litres (BMW) of its twin-turbo V8 rivals.

The Audi matches the M6 with 412kW of power, and betters it for torque (700Nm versus 680Nm). But the Benz’s big block trumps both with 430kW and 800Nm.

However, as the old cliché goes, it’s not the size that matters, but how you use it that counts – that’s seemingly the case for the all-wheel-drive Audi RS7, which has a quicker claimed 0-100km/h sprint time than both of its rear-drive rivals. Audi claims the RS7 can sprint from 0-100km/h in 3.9 seconds, while the Benz takes 4.1s and the M6 has a 4.2s claim. And the Audi is more efficient – claimed fuel use is 9.8L/100km, better than the BMW (9.9L) and the Benz (10.0L). Read the full specifications of the Audi RS7 Sportback here.

That V8 pushes out its maximum 412kW of power between 5700-6600rpm, but while it's not as high-revving as the RS4's non-boosted V8 (8250rpm) its 700Nm of peak torque is on tap from 1750-5500rpm, which makes for eye-watering acceleration.

We hardly explored the engine’s immense abilities – you’d need a racetrack or autobahn for such a feat – but it is a smooth-revving, muscled beast of a thing, with incredible throttle response and a scintillating soundtrack that mixes low-down growls and exhaust crackles. Check out the video above for that.

Unlike many other RS models, the RS7 is equipped with an eight-speed torque converter automatic transmission with paddle shifters. The ZF gearbox offers precise and quick gearshifts, and won’t overrule the driver if they wish to hit the rev limiter in manual mode.

We were impressed by its relative frugality, however – the engine features a cylinder deactivation system that can cut of four cylinders under light load, improving fuel use by 20 per cent, according to Audi. The system is unobtrusive, but clearly works as we beat its claimed fuel use of 9.8L/100km with a reading of 9.4L on our first test loop of mainly regional roads with the occasional spurt of acceleration. A more spirited drive loop saw that rise to 14.2L/100km, still respectable for what it is.

The car we tested featured Audi’s dynamic package including RS sport suspension with steel coils and adjustable dampers – a $4900 option over the standard air suspension setup. The floatier adaptive air setup could be more cossetting, but the steel spring setup offers both a relatively decent ride and immense roadholding.

The ride quality across patchy surfaces is nothing short of stellar given the RS7 sits atop standard 21-inch wheels with liquorice-thin 30-aspect tyres, though best to avoid the overly stiff Dynamic mode for commuting and opt for the Comfort or Auto modes that take a sufficient edge off bumps.

The steering is overly light in Comfort and occasionally inconsistent weighting can be noticeable, so some drivers may want to use the Individual mode that can tailor different settings for each parameter.

There's also an artificiality to the steering, though, which doesn't help connect the driver to car and road, yet it's direct and precise enough to help match driver confidence to the vehicle's fast cornering ability. The car’s heavy front-end does dull its agility through sharper direction changes, and under hard driving we noticed some slight understeer. It is, after all, a five-metre-plus, two-tonne machine. The quattro all-wheel-drive system helps keep things in order, directing torque to where it’s needed.

Inside, the RS7 Sportback is a comfortable and extremely well presented space. The interior carbonfibre finishes make it feel racy, while the quilted leather seats front and rear are supportive yet also comfortable enough to make it feel like a luxury cruiser.

On the topic of luxury, the Audi offers most of the right gear. There’s a standard sunroof, Audi’s MMI touch media system with satellite navigation, digital radio and TV reception, Bluetooth connectivity, an array of cameras around the car to help you park with confidence (which is important for a car of this size), and all of the main touch-points are covered in soft materials.

However, there are a few items that we’d suggest should be standard considering the price, such as ventilated front seats and radar cruise control – the former of which can’t be optioned although front seat heating is standard, and the latter of which is only available as part of a $10,375 assistance pack which also adds safety items such as a night vision, lane-keeping and blind-spot assistance systems.

Storage is generally well accounted for, but there are no large bottle holders in the doors. The boot features an auto opening and closing function and is quite large, too, at 535 litres – but the RS6 Avant could be a more practical option for pragmatic buyers as it offers better luggage capacity, more rear headroom, and a fifth seat – the RS7 only has four.

The wagon also saves $13,500 and is the CarAdvice team's preference even if it's understandable that many buyers will find the 'five-door coupe' RS7 more desirable.

Like the RS6, though, the RS7 still makes a convincing case as a fine all-rounder. While there are limitations to its ability to connect driver and car, and we have yet to test the standard air suspension, the fast four-door Audi still entertains - especially with its masterful twin-turbo V8 - and there's ride comfort you can live with daily. It also makes its key direct rivals look pricey in comparison.